The present invention relates generally to telecommunications systems and methods, and more particularly, a system and method for an improved optical regenerator.
Optically transparent packet data transmission technologies that provide access to the entire transport bandwidth (i.e., asynchronous transmission) while reducing or eliminating the costly synchronization provided by the traditional SONET/SDH layer have attracted attention following the tremendous growth of the internet (i.e., global computer network). In order to transport an optical signal over a long distance, the optical signal must be regenerated to avoid degradation of the signal that will occur over long distance transmission. This is accomplished using an optical regenerator.
Conventional signal regenerators are electronic devices comprising electrical components. As a result, current regeneration of the optical signal requires the optical signal to be converted to an electrical signal, regenerated using an electronic signal regenerator, the regenerated electrical signal is converted to an optical signal and the regenerated optical signal is forwarded over the optical network. The conversion from an optical to electrical signal requires a clock recovery circuit that synchronizes the input data clock rate in order to maintain the integrity of the signal payloads. Currently these clock recovery circuits require continuous (or synchronous) data without gaps between the data packets because the local clock and input data will become de-synchronized, resulting in errors (e.g., lost data) in the regeneration process. Therefore, these conventional electrical regenerators are not useful for asynchronous optical data networks.
Therefore, a need exists for an all transparent all-optical asynchronous optical signal regenerator that would maintain the optical signal quality when transporting optical signals across a large backbone asynchronous optical network. In such a transparent optical packet network, the optical packet payload could remain in the optical domain from the source to the destination in the network without suffering the optical/electronic conversions (and the associated conversion circuits), the data integrity problems and the associated bandwidth limitations (i.e., gaps between data packets can be tolerated during regeneration).
Recently, an all-optical asynchronous regenerator was proposed where traditional clock recovery is replaced by an asynchronous optical regenerator that regenerates the incoming packet while converting to the bit-rate of a local clock source. D. Cotter and A. D. Ellis, Asynchronous Digital Optical Regeneration and Networks, IEEE Journal of Lightwave Technology, Vol. 16, No: 12, pp 2068-2080, December 1998, hereby incorporated by reference in its entirety. The basic idea of this proposal is to use the incoming data pattern to trigger an all-optical xe2x80x9cgatexe2x80x9d from a set of multiple optical gates in parallel, and gate out optical pulses from a continuously running local optical oscillator (clock). The local oscillator is nominally operating at the data bit rate; hence a regenerated data is generated from the local clock source. In this proposal, discrimination of the local clock phase on a packet by packet basis needs to be performed. The authors propose to solve this issue by using several phase-shifted versions of the local clock, and gating the clock output with the maximum energy.
However, this proposed system has two distinct disadvantages: first, the proposed regenerator has an inherently high jitter (i.e., noise) that will result in degradation of the optical signal, and second, the number of optical gates in parallel required to reach a level of accuracy associated with current synchronous regeneration systems is very high. Thus, this proposed optical regenerator does not easily scale and the complexity of the optical regenerator increases dramatically when jitter tolerance is increased in order to achieve performance close to that of synchronous optical regeneration systems. While the jitter tolerance of this proposed asynchronous optical regenerator may be able to be improved, it would require the use of a large number of optical gates to sample the multiple local clock phases, thereby introducing signficant complexity into the regenerator architecture and requiring more space and numerous expensive optical gates. Also, the proposed solution requires the incoming signal to be split many times which causes a large optical insertion loss and reduced sensitivity of the optical regenerator. This prevents scaling beyond a certain level because the split signal will eventually approach the noise boundary. This may be able to be overcome by optical pre-amplification to compensate for this large splitter loss, however, this will require costly optical pre-amplification.
The present invention provides an asynchronous, low-jitter, optical regenerator that reduces complexity, is scalable and improves reliability.
More specifically, the present invention provides a system for regenerating an optical signal in a telecommunications network. The optical regenerator receives a generated multiple wavelength local clock signal and an input optical signal comprising asynchronous optical packets at an optical gating element. The input optical data causes a sampling of the multiple wavelength local clock signal at the optical gate. The optical domain sampled local clock signals are output on a single fiber. A demultiplexer splits the signal into a set of individual wavelength sampled local clock signals and outputs each onto a separate output fiber. The electrical energy of each is measured using an optical to electrical converter and a controller. Based on the highest energy level measured, a control signal is created and sent to an optical switch that selects the highest energy optical domain sampled local clock signal and passes it through as the regenerated signal.
The present invention provides an important technical advantage by providing an asynchronous optical regenerator that does not require optical-to-electronic conversion of an optical signal for the regeneration of the optical signal.
The present invention provides a technical advantage over previously suggested optical regenerators because it significantly reduces the complexity of the asynchronous optical regenerator while simultaneously increasing jitter tolerance to achieve performance compatible with that of a synchronous optical regenerator.
The present invention provides yet another technical advantage by eliminating the large input optical insertion loss due to the large passive optical splitter in previously suggested asynchronous optical regenerators. This eliminates expensive pre-amplifiers while improving the sensitivity of the asynchronous optical regenerator.